Geologists explore the Cave of Crystals (Cueva de los Cristales) in Naica Mine, Chihuahua, Mexico. (Image credit: JAVIER TRUEBA / MSF / SCIENCE PHOTO LIBRARY) The Cave of Crystals is an underground cavern filled with tree-size gypsum crystals, including some of the largest natural crystals ever found. The cave is located around 980 feet (300
